Fine bubble delivery for potable water, wastewater, and clean water treatment

ABSTRACT

A flexible tubing for fine bubble aeration is provided with an air passageway defined in part by an upper portion and a lower portion. The tubing can be made of a uniform weighted material with more material in the lower portion than in the upper portion. This makes the tubing self-orienting, in that it will tend to orient itself with micro-slits along the upper portion facing upward and the lower portion facing downward when submerged in a body of water. An automated, one-stage production line converts raw tubing material to a finished tubing product without the need for separate processing. A method of coiling the tubing places the micro-slits approximately 90° away from the surface of a spool hub, thereby avoiding a longitudinal arch in the tubing and ultimately preventing roll-over and improper slit orientation after installation in a water body.

CROSS REFERENCE TO RELATED APPLICATION

This application claims priority from and the benefit of ProvisionalPatent Application Ser. No. 60/740,355, filed Nov. 29, 2005, which ishereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to devices for purification andtreatment of bodies of water. More particularly, the invention relatesto weighted, flexible tubing which is submerged in a body of water foraeration of the water with small bubbles. Special application is foundfor this approach in natural bodies of water or in wastewater lagoonswhich are difficult or impractical to drain.

2. Description of Related Art

Aeration of a body of water is beneficial for a number of reasons. Forexample, it promotes the growth and survival of aerobic micro-organisms,intermediate life forms such as worms and snails, as well as fish andother aquatic wildlife and prevents ice from forming on docks and ships.Perhaps most importantly, aeration is an excellent way to naturallytreat wastewater without the introduction of chemicals or the need toremove, haul, and dispose of sludge. In nature, the rolling motion of ariver transports oxygen from the water surface to the bottom, whichsupports riverbed scavengers that digest organic waste and clean thewater by converting sludge into carbon dioxide and water. Aerationsystems recreate this natural process by providing tubing near thebottom of a body of water and supplying air flow through the tubing. Airslits or orifices in the wall of the tubing or outlet fixturesassociated with the tubing allow bubbles to escape into the water,thereby causing the surrounding water to move and circulate in a mannersimilar to the aforementioned natural rolling motion.

Modern aerators maximize efficiency and performance by providing smallbubbles, typically having diameters less than ⅛^(th) of an inch (3.175mm). This is much preferred to using larger bubbles, because largerbubbles rise quickly through the water, decreasing the contact timebetween air and water, and create turbulent flow, which can liftsediment off of the bottom surface and disperse it throughout the water.In contrast, smaller bubbles rise slowly and create laminar flow, whichincreases the residence time of the bubbles in the water withoutstirring up sediment.

Of course, residence time is increased by situating the aerators at thebottom of the water, but care must be taken to properly orient theaerators during installation. Optimal bubble generation is created whenthe bubbles are released from the uppermost part of the tubing. If thebubbles are instead released from a lower portion of the tubing, then itis possible that they will merge to form larger bubbles, therebydegrading the performance of the aerator. One approach to properlyaligning the tubing is to provide fixtures for immobilizing the tubing,such as the system of U.S. Pat. No. 6,511,054, which is herebyincorporated herein by reference. Another approach has been to providerigid tubing that will not move or rotate after it has been installed. Atypical aerator having such a construction can be seen in U.S. Pat. No.5,714,062, which is hereby incorporated herein by reference.

While these two approaches are effective in properly orienting thetubing, their usefulness is limited for a number of reasons. Aeratorsusing securing fixtures are generally limited to artificial bodies ofwater having substantially flat bottoms, in order for the tubing to beproperly oriented. Also, it is very difficult to service aerators thatare affixed to the bottom of the body of water. As for aerators havingrigid tubing, they are relatively expensive and, if they are not securedto the bottom of the body of water, then substantial efforts must betaken to ensure that they are submerged at the proper orientation andremain so oriented.

An alternative approach is to provide tubing that orients itself afterbeing submerged. Such an aerator is shown in U.S. Pat. No. 3,293,861,which is hereby incorporated herein by reference. Such an aeratortypically includes flexible tubing with a series of micro-slits and aballast wire diametrically opposing each other along a length of thetubing. The ballast wire causes the tubing to remain submerged, evenwhen filled with air, and automatically places the micro-slits at theuppermost part of the submerged length of tubing.

Such weighted flexible tubing is preferable to the previously describedsystems, because it is capable of transferring more oxygen per hp-hourand pumping more gallons of water per hp-hour for many aerationoperations, such as deep water installations. However, flexible tubingaccording to the prior art is difficult and expensive to manufacture andoften results in a great deal of wasted wire material. Known flexibletubing includes that manufactured according to a multi-stage process,whereby a thin-walled tube is first extruded to define an airpassageway. The thin wall makes it difficult to achieve and maintainduring manufacture, installation and use, an air passageway with a trulycircular cross-section, and any resulting tube that is not substantiallytubular or has an overly thin or thick wall can be rejected as defectiveor perform with reduced efficiency. When the air passageway has beensuccessfully formed, the tube is passed through the extruder a secondtime, with a ballast wire pressed thereagainst. By this approach, thetube and ballast wire are joined together by the extruder with a film orskin (typically comprised of the same material as the tube) surroundingtheir outer surfaces.

After the tubing of this type is thus formed, it typically would be sentto another facility or production line to add micro-slits to the airpassageway. The wire keel protrusion makes it difficult to properlyalign the tubing, which can lead to irregularly spaced, sized, andpositioned slits. Furthermore, tubing using a lead ballast wire is evenmore problematic due to the known harm that lead can cause to theenvironment and those who handle it. In fact, lead-weighted tubing isprohibited by the U.S. Environmental Protection Agency for use intreating bodies of potable water, even if the lead is fully encapsulatedby a non-toxic layer.

Another problem with prior art flexible tubing systems is that theygenerally have a wall thickness no greater than 0.10-0.20 inch (2.54mm-5.08 mm). Most often, same is in the range of 0.055-0.075 inch (1.397mm-1.905 mm). This results in nominal orifice pressure drop, causinguneven air distribution and difficulty controlling bubble size. Also, itis difficult to adequately clean such tubing systems, because a cleaningsolution injected into the tubing will be released through the initialslits, while little or no solution remains in the tubing to reach andclean the slits at a far end of the tubing. Finally, thin-walled tubingsystems are especially prone to kinking, puncturing, collapsing,tearing, cracking, and other performance-inhibiting maladies caused bytransport, installation, temperature extremes, high pressure at greatsubmersion depths, abuse by animals, long-term use, and the like.

Yet another possible drawback of using known thin-wall flexible tubingis lifting it from a body of water for inspection or servicing. Knownflexible tubing that has become buried in sludge, mud, gravel ordebris—for example, as little as 1-3 inches (2.54 cm-7.62 cm) of sludgecoverage—is likely to kink, fold, or break when removed by known meansand methods, such as a “J” hook or clamping fixture of a boat. Suchdamage to the tubing degrades the performance of the air-cuts, even ifmanufactured to provide preferred bubble formation, with a negativeresult of having the system “boil” air. When this occurs, the treatmentsuffers and the tubing needs replacing.

Accordingly, a general object or aspect of the present invention is toprovide an improved flexible tubing system for fine bubble aeration.

Another object or aspect of this invention is to provide flexible tubingthat is self-submerging and self-aligning without the use of a ballastwire.

Another object or aspect of this invention is to provide flexible tubingwith improved durability.

Another object or aspect of this invention is to provide an improvedmethod of manufacturing a flexible tube for fine bubble aeration,typically maintaining oil-less fine bubble release in the top area ofthe tubing as it rests on or near the bottom of a body of water when inuse.

Another object or aspect of this invention is to provide a method forcoiling and/or storing a flexible tube for fine bubble aeration.

Another object or aspect is to reduce costs for running aeration systemsto treat water and wastewater, preferably without using toxic materialssuch as lead, including during manufacture, installation or long-termuse in water systems.

Other aspects, objects and advantages of the present invention,including the various features used in various combinations, will beunderstood from the following description according to preferredembodiments of the present invention, taken in conjunction with thedrawings in which certain specific features are shown.

SUMMARY OF THE INVENTION

In accordance with the present invention, a flexible tubing for finebubble aeration includes an air passageway defined by an upper portionwith a larger profile or a widened profile such as a generally arcuateprofile and a lower portion with a generally squared profile. The tubingtypically is constructed of a substantially uniform mixture of plastics,polymers or rubber-like compounds and a high-density mineral to overcomebuoyancy. For example, the rubber-like material may be highly filledvinyl compounds, PVC, polyethylene, polypropylene, polystyrene, or thelike, and the high-density material may be barium sulfate or a similarsafe dense mineral. Preferably, the mixture allows different lengths oftubing to be glued or fastened together, while the unique larger,widened or heavier lower portion assures proper alignment of themicro-slits when joining separate lengths of tubing.

The tubing is self-submerging due to the presence of the high-densitymaterial and is also self-orienting. There is more material bulk or massin the lower portion than the upper portion, so the tubing isbottom-heavy and will align itself with the larger, widened or heavierlower portion pointing downward. Micro-slits are placed along thearcuate upper portion, so they will face upward after the tubing hasoriented itself in a body of water.

Preferably, the tubing walls are relatively thick, with the upperarcuate portion being at least 0.15 inch (3.81 mm) thick and up to 1.50inches (3.81 cm) thick. The performance of the micro-slits of the upperarcuate portion is enhanced by the thicker wall, which makes the slitsmore durable and resistant to deformation due to foreseeable use andabuse. The greater thickness also causes an increased pressuredifferential, typically a minimum internal pressure drop of 2 PSI, whichprevents performance degradation in bodies of water having sloped orinclined bottom surfaces.

A method of manufacturing tubing according to the present invention maybe accomplished on a single automated line, which processes the tubingfrom formation to coiling. A selected mixture of tubing material isadded to a hopper, where the mixture is extruded into a tube shape andcured, typically by cooling and drying processes. Micro-slits are added,and the tubing is coiled onto a spool. Additional steps may include amarking process to visually identify an upright position of the tubing.

The slits are preferably precise, surgical cuts in a straight line alongthe upper portion of the tubing. The slits are formed without removingany material or leaving any burrs, and the generally rubber-likeconstruction of the tubing imparts an elastic wall memory, so themicro-slits will close tightly when there is no air flowing through thetubing. Thus, the cuts act like check valves to protect themselves andthe air passageway from the inflow of debris and settled solids. Whencombined with a thicker wall, the micro-slits perform even better ascheck valves and will snap shut after airflow is terminated.

The tubing is coiled about a spool such that the micro-slits and squaredlower portion are each approximately 90° from the spool hub. Thus, therewill be no arch along the length of the tubing, which will remainsubstantially flat, thereby preventing micro-slit deformation,involuntary roll-over, and other performance degradation. Any lateralcurvature in the tubing is minimized by soft tension coiling, whichreduces the risk of puckering or other deformation of the slits.

Additional performance and cost benefits of tubing according to thepresent invention are derived from its simplicity and unique power costeffectiveness. For example, the tubing can biologically convert unwantedwastes in the water into useful biota, carbon dioxide, and pure waterwith only 1-2% inert ash residual. Also, it is estimated that tubingaccording to the present invention reduces the costs of operating anassociated blower/compressor of systems using this type of tubing to arange of about $0.01 to $0.02 per capita per day for lagoon treatmentand to a range of about $0.04 to $0.08 per capita per day for activatedsludge treatment.

The streamlined manufacturing and installation processes, along with thereduced operating costs, are estimated to substantially reduce activatedsludge treatment costs. For example, for a small-to-medium sizedcommunity (500-10,000 people), such costs can be reduced from a $5-$10per gallon range to a $1-$2 per gallon range. It will be appreciatedthat cost reductions are also realized during retrieval and inspectionoperations due to the durable design according to the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a cross-sectional view of a flexible tube according to anaspect of the present invention;

FIG. 1B is a cross-sectional view of another flexible tube according toan aspect of the present invention;

FIG. 1C is a cross-sectional view of yet another flexible tube accordingto an aspect of the present invention;

FIG. 2 is a perspective view of a flexible tube according to an aspectof the present invention;

FIG. 3 is a cross-sectional view of a flexible tube according to anaspect of the present invention, with a micro-slit;

FIG. 4A is a cross-sectional view of a flexible tube according to anaspect of the present invention, with a micro-slit in an open position;

FIG. 4B is a cross-sectional view of the flexible tube of FIG. 4A, withthe micro-slit in a closed position;

FIG. 5A is a perspective view of two tubes and a tube insert connector;

FIG. 5B is a perspective view of the two tubes of FIG. 5A, joined by thetube insert connector;

FIGS. 6-6B illustrate an automated, in-line manufacturing processaccording to an aspect of the present invention;

FIG. 7A is a side view of a tube wound on a spool in a conventionalorientation;

FIG. 7B is a perspective view of the tube of FIG. 7A, in an uncoiledconfiguration;

FIG. 7C is a perspective view of the tube of FIG. 7B in a roll-overcondition;

FIG. 8A is a side view of a tube properly wound on a spool according toan aspect of the present invention;

FIG. 8B is a perspective view of the tube of FIG. 8A, in an uncoiledconfiguration;

FIG. 9A is a perspective view of a tube having a secondary lumen and apair of tethers;

FIG. 9B is a cross-sectional view of another embodiment of a tube havinga secondary lumen and a pair of tethers;

FIG. 9C is a perspective view of an embodiment of a tube having a pairof tethers;

FIG. 9D is a perspective view of an embodiment of a tube having asecondary lumen;

FIG. 9E is a perspective view of an embodiment of a tube having aplurality of secondary lumens;

FIG. 9F is a cross-sectional view of an embodiment of a tube having a“modified D-shaped” profile and a plurality of secondary lumens andtethers;

FIG. 10A is a perspective view of a tube according to an embodiment ofthe present invention having an alternative air-cut slit arrangement;

FIG. 10B is a perspective view of a tube according to the presentinvention having yet another alternative air-cut slit arrangement; and

FIG. 10C is a bottom perspective view of the tube of FIG. 10B, withselected portions broken away.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As required, detailed embodiments of the present invention are disclosedherein; however, it is to be understood that the disclosed embodimentsare merely exemplary of the invention, which may be embodied in variousforms. Therefore, specific details disclosed herein are not to beinterpreted as limiting, but merely as a basis for the claims and as arepresentative basis for teaching one skilled in the art to variouslyemploy the present invention in virtually any appropriate manner.

FIGS. 1A-4B show several possible embodiments of a flexible tubing 10according to respective aspects of the present invention. The flexibletubing 10 has an outer cross-sectional profile defined by asubstantially semicircular upper portion 12 and a rectangular or squaredlower portion 14 having two flat sidewalls 16 extending downwardly fromthe arcuate upper portion 12 and a flat bottom wall 18 extending betweenthe sidewalls 16. The illustrated tubing cross-section is referred toherein from time to time as a “D-shaped” profile because it resembles anupper-case “D”. When installed, the “D-shaped” profile is rotated 90°counterclockwise. As illustrated in FIGS. 1A-4B, the upper and lowerportions 12 and 14 preferably are sized and configured to merge togetherwithout any seams or discontinuities. FIGS. 1A and 1C illustrate tubing10 with upper and lower portions 12 and 14 having the same height, butthe heights may be different, as shown in FIG. 1B.

Preferably, the tubing 10 is constructed of a substantially uniformmixture of plastics or rubber-like compounds and a high-density mineralto overcome buoyancy. For example, the rubber-like material may behighly filled vinyl compounds, PVC, polyethylene, polypropylene,polystyrene, or the like, and the high-density material may be bariumsulfate or a similar safe heavy compound, material or mineral. In aspecific embodiment, the tubing material is a blend of UV-resistant PVCpolymers with plasticizers and barium sulfate resulting in a specificgravity of approximately 1.99 SG that ensures the tubing is non-buoyantin a water body. In another embodiment, the lower portion 14 iscomprised of a material blend having a greater specific gravity than theupper portion 12 to encourage proper orientation during installation.The mixture of materials makes the tubing flexible, damage-resistant,UV-protected, heat- and cold-protected, and non-toxic. It is estimatedthat tubing according to the present invention is sufficiently durableto withstand turbulent and/or corrosive water conditions for 20 yearswithout failure or significant performance degradation.

While tubing comprising a blend of a plastics, polymeric or rubber-likematerial combined with high-density mineral or material as describedherein may be preferred, it will be seen from the following descriptionthat several aspects of the present invention may be practiced withtubing wholly comprised of a plastics, polymeric or rubber-likematerial. Of course, if the tubing is so provided, care should be takento assure that the specific gravity is sufficient to render the tubingnon-buoyant in a water body.

The tubing 10 includes an air passageway 20, through which air may bepumped through the tubing 10, typically by operation of blower and/orcompressor equipment. As illustrated in FIGS. 1A and 1B, the airpassageway 20 is preferably concentric with the arcuate upper portion12, but it need not be, as shown in FIG. 1C. The portion of the tubing10 above the center longitudinal axis of the air passageway 20 definesthe upper portion 12, while the portion below the center longitudinalaxis defines the lower portion 14. An important aspect of the presentinvention is that there is more material in the lower portion 14 than inthe upper portion 12, such that the lower portion 14 is heavier andtends to orient itself under the upper portion 12 when submerged in abody of water. Hence, the air passageway 20 must be properly placed inorder for the tubing 10 to remain bottom-heavy, otherwise theself-orienting function will be disrupted.

FIGS. 1A-1C illustrate an uncut profile of the tubing 10. The upperportion 12 includes a plurality of longitudinally spaced micro-slits orslits 22, as shown in FIGS. 2-4B. Preferably, the slits 22 are surgicalcuts with smooth faces 24 (FIG. 4A), so no material is removed and thereare no burrs or bumps between opposing faces. When air is pumped throughthe air passageway 20, it will escape through the micro-slits 22, whichgenerally take on the open condition of FIG. 4A, and will be releasedinto the surrounding environment. Optimal aeration performance isachieved by laminar flow of relatively small bubbles, so the slits 22are placed at an uppermost portion 26 of the tubing 10 and are sized andconfigured to release bubbles having a diameter between 1/64 inch and ⅛inch (between about 0.397 mm and 3.175 mm).

When no air is being pumped through the tubing 10, the slits 22 take onthe closed condition of FIG. 4B, due to the elastic wall memory of thetubing material. The precisely formed slits 22 substantially close toprevent water or waste solids even as small as 0.001 inch (0.0254 mm) indiameter from entering the interior of the tubing 10. This valvingfunction of the slits 22 is enhanced by a relatively thick upper tubewall 28, which is five to ten times thicker than other previousapproaches. The tube wall 28 provides a larger wall surface area andcauses the slits 22 to close tighter than for a thinner upper tube wall.In a preferred embodiment, the upper tube wall 28 is between 0.20 inchand 0.30 inch (between about 5.08 mm and 7.62 mm) thick for a tube 10having an air passageway 20 with a 0.50 inch (1.27 cm) diameter. For atube 10 having a larger air passageway 20, such as 0.75 inch (1.905 cm)or 1.50 inches (3.81 cm), the upper tube wall 28 is preferably between0.50 inch and 1.50 inches (between about 1.27 cm and 3.81 cm) thick.

By way of further illustration, the pipe dimension ratio or “DR” is avalue established by the American Society for Testing and Materials(ASTM) to express the relative wall thickness, and hence the pressurerating, of a pipe or tube. The dimension ratio is equal to the outerdiameter divided by the minimum wall thickness of the tubing, and thepressure rating increases as the dimension ratio decreases. For knownflexible aeration tubing, the dimension ratio is typically in the rangeof approximately 10-11. For example, a known flexible aeration tubinghas an outer diameter of 0.625 inch and a wall thickness of 0.060 inch,for a DR of 10.4. In contrast, tubing according to the present inventionmay have a dimension ratio of approximately 5 (for the above example ofa tube having an upper wall thickness of approximately 0.50 inch and anair passageway diameter of approximately 1.50 inches, or an outerdiameter of 2.50 inches) or less. Another embodiment has an outerdiameter of 0.950 inch and a wall thickness of 0.250 inch, for a DR of3.8.

In addition to enhancing the valving function of the micro-slits 22, theuse of a thicker upper tube wall 28 provides numerous other advantages.For example, the tube 10 is more durable and will resist kinking ortearing or other deformation, which ensures the functioning of themicro-slits 22 as designed. This tubing 10 is stronger, more reliable,and less likely to collapse, crack or damage the air cuts 22. Thickertube walls 28 also allow the tubing 10 to function in deeper water,e.g., at depths of between 33 feet and 100 feet (between about 10.06 mand 30.48 m), without collapsing. Also, the wall 28 compresses thebubbles before they are released into the surrounding environment.

By this feature, tubing according to the present invention is much morereliable than known tubing in terms of limiting the size of bubbles andpreventing the “coning effect.” The “coning effect” refers to asituation whereby bubbles larger than ⅛ inch (3.175 mm) slip through theorifices and fail to lift the surrounding water nearly as much asproperly sized bubbles. In extreme cases, larger bubbles will lift 4-6times less water than properly sized bubbles. This is as important asbubble contact time for transfer of oxygen into the water, because it isimportant to disperse the oxygen equally throughout the water body.Ultimately, this feature reduces the electrical power required for thebubble-formation system to maintain uniform dissolved oxygen all overthe water column and not just above the diffuser. Over a 20-year timeperiod, the electrical costs to run the associated blower/compressorusually is the single largest cost of aerating a body of water, so areduction in power requirements without a reduction in performance is amajor benefit.

Furthermore, a relatively large pressure differential is created betweenthe air passageway 20 and the outside environment, which improves fluiddynamics and allows for a more uniform distribution of air and cleaningfluid, especially at a distal end of the tubing 10. Typically, theminimum internal pressure drop at the slits 22 is at least 2 PSI, whichallows for a 4.6 foot (about 1.4 m) end-to-end height variation of aninstalled tube without a loss of air pattern. In one exemplaryapplication, tubing according to the present invention allows for bubbleuniformity of plus or minus 5-10% at every orifice for tubing lengths inthe range of 250-500 feet (76.2 m-152.4 m), which is difficult orimpossible to achieve with known tubing technology. Thus, the fluiddynamic properties of air flowing through thick-walled slits offersbetter control of the internal and external pressure differential andbetter control of uniform fine bubble release across long distances andnon-level bottom diffusion areas. Thick-walled tubing also avoids theneed to follow so-called soft-tension coiling or loose coiling of thinwalled tubing often required to prevent puckering of the air-cuts.

Lengths of tubing 10 according to the present invention may be joined byan adhesive or glue, as illustrated in FIGS. 5A and 5B, and the thickertube walls 28 provide more surface area on which to apply the adhesive.Furthermore, the widened or heavier lower portion 14 allows the lengthsof tubing 10 to be easily aligned, which ensures that the micro-slits(not illustrated) remain at the uppermost portion of the tubing 10.Preferably, this lower portion 14 has a squared profile, as illustrated.In addition to adhesive, the tubing sections 10 are preferably joinedusing a tube insert connector 30, which aids in aligning the sections 10and decreases the risk of leakage. It will be seen that flexible tubingaccording to the present invention is preferred to tubing having aballast wire, because it can be cut and joined to another length oftubing or a feeder without having to trim the wire or any excess skincoating and does not require special tools, clamps, or skill. For thesame reason, the tubing can be easily cut to the desired length duringmanufacture, which eliminates waste.

In addition to joining separate lengths of tubing, adhesive may also beused to repair a rupture or tear in the tubing. Known flexible tubing istypically comprised of polyethylene, which must be repaired by specialheat fusion or splicing tools. In contrast, tubing according to thepresent invention made of, for example, PVC may be repaired by dryingthe damaged area, priming any damaged air-cuts with primer, applyingadhesive to the area, and allowing the adhesive to set. Thus, tubingaccording to the present invention may be repaired by non-specialistsusing easily-accessible materials.

Tubing according to the present invention may be manufactured usingknown methods. A suitable and usually preferred manufacture by anautomated, one-stage production line 32 according to another aspect ofthe present invention is illustrated in FIG. 6.

The production line 32 includes a hopper 34, a heated barrel 36, anextrusion die 38, a curing vessel 40, a cutting unit 42, and a coilingstation 44. As can be seen, the tubing goes from raw material 46 to acoiled finished product 10 in one stage, thereby greatly reducingmanufacturing time, manpower, cost, and waste over the processes used tomanufacture tubing with a ballast wire. Stocking of only four basicdiffusion tubes satisfies needs for most water treatment applications,thereby simplifying inventory control and reducing costs.

The first step of this illustrated approach is to place a mixture of rawtubing material 46 into the hopper 34. The tubing material 46 can bestored in pellet form and added in different percentages, depending onthe intended use of the tubing. For example, there may be differentpre-mixes for wastewater treatment installations, as opposed to lake andreservoir, fish farming and aquaculture, and ice melting installations.Special mixes can be made to order as well, depending on the uniqueneeds of each body of water. It will be appreciated that tubingaccording to the present invention requires less storage space, becausethe raw materials can be completely stored in pellet form and noseparate space is required for coils of ballast wire.

After the desired mixture 46 has been added to the hopper 34, thepellets are fed through a heated barrel 36 and forced through anextrusion die-block 38 having a profile or opening correspondinggenerally to the “ID-shaped” profiles of FIGS. 1A-1C. Of course, theopening of the die 38 will have a different shape, corresponding forexample to the tube profile shown in FIG. 9F, if the cross-sectionalprofile of the tubing varies from the profiles of FIGS. 1A-1C. Asillustrated in FIG. 6A, the opening of the die-block 38 is rotated 90°with respect to the orientation of FIGS. 1A-1C. This orientation isimportant for properly winding the tubing, as will be described herein.

The tubing material forced through the die-block 38 is then fed througha curing vessel 40, where it is cooled and solidified. When the materialhas been sufficiently cured, it is passed through a cutting unit 42. Asshown in FIG. 6, the cutting unit 42 is aligned with the die-block 38,such that slits are made in the uppermost part of the arcuate portion ofthe tube, opposite the flat or widened bottom wall (as in FIGS. 2-4B).In accordance with the foregoing description, the cutting unit 42preferably creates surgical cuts in a straight line along the upperportion 12 of the tubing 10 without removing any tubing material orleaving any burrs. As opposed to prior art tubes, with ballast wireprotrusions that track poorly, the flat walls of the tubing according tothe present invention allow for better tracking and are easily alignedfor accurate slit placement. It is estimated that the amount ofdefective tubing produced by the method of FIG. 6 can be reduced fromapproximately 25% (for thin-walled flexible tubing with a ballast wire)to approximately 2-4% or less.

The cutting unit may include an ink-marking step before the slits areadded to the tubing. The ink-marking step adds registration marks 48 tothe arcuate portion 12 of the tubing 10 (FIG. 2), which are useful asadditional visual indicators of the orientation of the upper portion 12of the tubing 10.

After the micro-slits have been added to the tubing 10, the tubing 10 isfed to a coiling station 44. The coiling station 44, in the orientationshown in FIG. 6, has a horizontally-oriented spool 50 with a cylindricalhub 52. The tubing 10 is wound around the hub 52 for storage andtransport. According to an aspect of the present invention, the flat orwidened bottom wall 18 and the micro-slits 22 are disposed approximately90° away from the hub 52, as illustrated in FIGS. 6B and 8A. As thetubing 10 is continuously wound about the hub 52, it remains in theproper orientation, due to the tubing 10 being formed and wound as partof a one-stage process. This orientation is important to ensure that thetubing 10 remains longitudinally flat after installation as shown inFIG. 8B. Any lateral curvature in the tubing is minimized by softtension coiling, which reduces the risk of puckering or otherdeformation of the slits.

If the tubing 10 is instead wound such that the flat or widened bottomwall 18 is adjacent to the hub 52, as in FIG. 7A, then the coil memoryof the tubing 10 will result in a longitudinal arch 54, which is shownin FIG. 7B. An arch 54 makes the tubing 10 unstable and may cause it toroll over when uncoiled (FIG. 7C), which moves the micro-slits 22 awayfrom their optimal position and degrades the aeration capabilities ofthe tube 10.

Additional features and components may be incorporated into the tubingwithout departing from the scope of the present invention. For example,a secondary lumen or passageway 56 may be formed in the lower portion14, preferably directly below the air passageway 20 (FIGS. 9A, 9B, and90). As shown, the secondary lumen 56 may be substantially smaller thanthe air passageway 20. The secondary lumen 56 may be provided as atubular member embedded in the lower portion 14 (FIGS. 9A and 9D) or asa hollow lumen (FIG. 9B), similar to the air passageway 20. Thesecondary lumen 56 may be incorporated into the tubing 10 by any of anumber of methods, depending on the structure. If the secondary lumen 56is provided as a tubular member, it is preferably extruded into thebottom portion 14 during the method illustrated in FIG. 6. Suitablematerials for a tubular member include, but are not limited to highlyfilled vinyl materials, such as those used as tubing material accordingto an aspect of the present invention.

In one embodiment, the secondary lumen 56 runs the length of the tubing10 and has a diameter in the range of approximately 1/32- 1/20 inch(about 0.794 mm-1.27 mm) to allow air, gasses, and/or liquids to passtherethrough. The secondary lumen 56 may be used for any of a number ofapplications, such as carrying a fluid, for example air or another gas,to inflate a submerged flotation device (not illustrated) for retrievalof the tubing 10. In such an application, it is preferred for thesecondary lumen 56 to be sealed from the air passageway 20 and theoutside environment, as in FIG. 9A. For such an application, it may bepreferred for the secondary lumen 56 to be provided as a tubular member,with a portion thereof extending beyond the proximal and/or distal endsof the tubing to simplify fixation to the flotation device.

The tubing 10 of FIG. 9A may also be used in delivering nitrogen- and/orsludge-combating bacteria to the water column and/or sludge layer. Byknown methods, such bacteria are delivered to one or more of the surfaceof the water body, the water column, and the sludge, typically from aboat- or shore-based applicator. Hence, it will be seen that this aspectof the present invention advantageously allows the bacteria to be easilydispersed with a tube that has already been installed for aerationpurposes.

In another application, the secondary lumen 56 includes a plurality oforifices 58 (FIG. 9B) at selected locations along the length of thetubing 10 to allow for communication with the air passageway 20. Theorifices 58 may be provided in a number of configurations, such asmicro-slits or micro-fittings, and are preferably movable between aclosed condition, preventing communication between the secondary lumenand the air passageway, and an open condition, allowing communicationtherebetween. A cleaning or treatment fluid is passed through thesecondary lumen 56 and released through the orifices 58 to clean ortreat the air passageway 20 and air-cut slits 22. The orifices 58 of thesecondary lumen 56 may have a higher cracking pressure than the air-cutslits 22 to prevent the orifices 58 from opening during aeration of awater body.

The tubing 10 may also be provided with a plurality of secondary lumens56, as shown in FIGS. 9E and 9F. The secondary lumens 56 may provided aseither hollow tubular members, hollow lumens (FIG. 9E), or as acombination thereof (FIG. 9F). Also, the secondary lumens 56 may beseparate from each other along their lengths or may be joined at variouslocations by hollow or valved branches (not illustrated). The secondarylumens 56 may be used for different purposes, for example, one may beused for inflating a submerged flotation device, another may be used forapplying a cleaning fluid to the air passageway 20, and yet another maybe used for delivering nitrogen- and/or sludge-combating bacteria to atarget site.

FIGS. 9A and 9B also illustrate the tubing 10 with a pair of identicaltethers or harness cables 60 embedded in the lower portion 14.Alternatively, the secondary lumen 56 and tethers 60 may be practicedseparately, as in FIGS. 9C and 9D, and the tubing 10 may be providedwith a single tether, more than two tethers, or non-identical tethers.The tethers 60 preferably run at least the length of the tubing 10 and,more preferably, extend beyond the proximal and distal ends thereof.Alternatively, each illustrated tether 60 may be provided as two or moretether segments (not illustrated) axially aligned with each other andspaced along the length of the tubing or press-fit into cavities formedat the ends of the tubing (not illustrated). The tethers 60 may beincorporated into the tubing 10 by any of a number of methods, but arepreferably extruded into the bottom portion 14 during the methodillustrated in FIG. 6.

The tethers 60 are preferably comprised of a non-toxic, non-corrosivematerial that is stronger than the tubing material, such as stainlesssteel, and may have a diameter of approximately 0.0625 inch (1.5875 mm)for example. Other tether materials may also be used without departingfrom the scope of the present invention. If the tether material has agreater specific gravity than the tubing material, the tethers 60 willassist the lower portion 14 in properly orienting the tubing 10 within awater body. Accordingly, it may be preferred for the tethers 60 to besymmetrically arranged with respect to the width of the tubing 10, asillustrated in FIGS. 9A and 9B, to ensure that the tubing 10 isinstalled with the micro-slits 22 facing upwardly.

The tethers 60 may be used for any of a number of applications, such asto secure the tubing 10 to a submerged anchor (such as a post with aneye-bolt) and prevent movement thereof under strong underwater flow orcurrents such as mechanical pumping operations, strong river currents or“washout” rain falls. The tethers 60 may also be gripped to reel in thetubing 10 for inspection or servicing. In one embodiment, the tethers 60extend between one and four inches (between about 2.54 cm and 10.16 cm)beyond the ends of the tubing 10, but they may extend to a greater orlesser extent without departing from the scope of the present invention.

The use of secondary lumens and/or tethers may decrease the weightand/or effective specific gravity of the lower portion, so it may bepreferred to provide tubing having a modified lower portion to ensurethat the submerged tubing will properly orient itself. For example, FIG.9F illustrates tubing 10 a having a “modified D-shaped” cross-sectionalprofile, wherein the sidewalls 16 a extend downwardly and laterallyoutward from the upper portion 12 a to a bottom wall 18 a that is widerthan a width or outer diameter of the upper portion 12 a. In comparisonto the “O-shaped” profiles illustrated in FIGS. 1A-4B, the bottomportion 14 a of FIG. 9F has a greater height, which increases the weightof the bottom portion 14 a. When desired, this greater weight can bechosen so as to overcome any buoyancy that may be added by the secondarylumens 56 and/or tethers 60.

A “modified D-shaped” profile may also be practiced without secondarylumens or tethers and with a bottom portion height comparable to thebottom portion heights illustrated generally in FIGS. 1A-4B. Inparticular, tubing having a relatively wide bottom wall will have evenless tendency to tip over and become disoriented in turbulent waterconditions. Weight added by a more substantial bottom portion also canmaintain the tubing in an upright orientation, such as illustrated inFIG. 9F, or the added weight can combine with the relatively wide bottomto facilitate proper upright orientation.

Therefore, it may be preferred to provide flexible tubing having abottom wall at least approximately 50% wider than the width or outerdiameter of the upper portion. In another embodiment, the tube has a“modified D-shaped” profile with a bottom wall approximately twice aswide as the width or outer diameter of the upper portion. Otherembodiments have a bottom wall width suitable for the particular needsof the system, such as between about 150% and 200% and above of theupper portion width or diameter.

It will be appreciated that the secondary lumen and/or tethers may beinitially manufactured to extend beyond the ends of the tubing or mayinstead be coextensive or somewhat shorter than the tubing, in whichcase the ends of the tubing may be trimmed or cut away to expose aportion of the secondary lumen and/or tethers. Therefore, the terms“proximal end” and “distal end,” when referring to a tubing according tothe embodiment of FIG. 9, are used broadly to refer to either thestructure of the tubing as manufactured or as submerged in a body ofwater. Additionally, it will also be appreciated that secondary lumensand tethers according to this aspect of the present invention may beincorporated into known flexible tubing, although it may be preferred touse them in combination with tubing according to the present invention.

Finally, FIGS. 10A-10C illustrate additional embodiments of tubing 10according to the present invention. The tubing 10 of FIGS. 10A-10Cincludes micro-slits 22 arranged in a line along the uppermost portion26, as well as micro-slits 22 a formed at locations of the upper portion12 angularly spaced from the uppermost portion 26. In FIG. 10A, all ofthe micro-slits 22, 22 a are formed in the same plane, whereas themicro-slits 22, 22 a are staggered along the length of the tubing 10 ofFIGS. 10B-10C. As illustrated, it may be preferred for the micro-slits22, 22 a to be equally spaced from each other along the length of thetubing 10, but the spacing may vary without departing from the scope ofthe present invention. While many applications may be best served bymicro-slits aligned along the uppermost portion 26 of the tubing 10,other applications may benefit from micro-slits aligned along a lineangularly spaced from the uppermost portion 26 or micro-slits arrangedat varying angular positions along the length of the tubing 10. Hencetubing according to the present invention is not limited to a specificmicro-slit placement, orientation, or arrangement.

It will be understood that the embodiments of the present inventionwhich have been described are illustrative of some of the applicationsof the principles of the present invention. Numerous modifications maybe made by those skilled in the art without departing from the truespirit and scope of the invention, including those combinations offeatures that are individually disclosed or claimed herein.

1-12. (canceled)
 13. A method of manufacturing a flexible tubing forfine bubble aeration, comprising: providing a raw tubing material;extruding the tubing material into a flexible tubing having an upperportion of a given cross-sectional area, a lower portion of a selectedcross-sectional area larger than said given cross-sectional area of theupper portion, and a longitudinal air passageway defined by the upperand lower portions; curing the flexible tubing; and cutting micro-slitsthrough the upper portion of the flexible tubing, wherein saidextruding, curing, and cutting are performed by an automated, one-stageproduction line.
 14. The method of claim 13, further comprising markingthe tubing to indicate the orientation of the upper portion, whereinsaid marking is performed by the automated, one-stage production line.15. The method of claim 13, further comprising coiling the flexibletubing onto a spool having a cylindrical hub while orienting theflexible tubing to engage a side portion of the upper portion and a sideportion of the lower portion of the flexible tubing.
 16. The method ofclaim 15, wherein said coiling is performed by the automated, one-stageproduction line.
 17. The method of claim 13, wherein said cuttingmicro-slits through the upper portion of the flexible tubing includesmaking surgical cuts without removing any tubing material or withoutleaving any burrs.
 18. The method of claim 13, wherein said extrudingthe tubing material includes passing the tubing material through agenerally “D-shaped” opening of an extrusion die.
 19. The method ofclaim 13, wherein said extruding includes defining a secondary lumen inthe lower portion, said secondary lumen being adapted for passing afluid or gas therethrough when the tubing is submerged in a body ofwater.
 20. The method of claim 13, wherein said extruding includesembedding at least one tether into the lower portion, said at least onetether being adapted for securing the tubing when submerged in a body ofwater. 21-31. (canceled)
 32. The method of claim 13, wherein saidextruding the tubing material includes extruding the tubing materialinto a flexible tubing having a lower portion comprising across-sectional shape with generally flat sidewalls and a generally flatbottom wall extending between the sidewalls.